A RAM disk is a block of RAM that is treated as if is secondary storage.

Random access memory is primary storage and is accessible directly by the CPU. However there are occasions when RAM is accessed by a computer's software as if it is secondary storage and is made available as a RAM disk.

A RAM disk should not be confused with a RAM drive or solid-state drive. It is sometimes referred to as a virtual RAM drive or software RAM drive to distinguish its use of primary storage from a hardware RAM drive that uses separate hardware containing RAM.

Because storage in RAM is extremely fast, files in a RAM disk can be accessed very quickly. However, because the storage is in RAM, it is volatile and is lost when the computer is turned off. In many cases data in a RAM disk is created from data permanently stored elsewhere, and is re-created on the RAM disk each time the system boots.

Implementation

A RAM disk uses RAM as if it is a volume in secondary storage. RAM disks are often supported from the operating system via special mechanisms in the kernel; it is also possible to create and manage a RAM disk using a user space program.

Some RAM disks use a compressed filesystem such as cramfs to enable compressed data to be accessed without uncompressing it first. This is convenient because RAM disks are often small.

It is possible to store a web cache in a RAM disk to improve the speed of loading pages.